Concurrent multi-loudspeaker calibration

ABSTRACT

Examples involve calibration of two synchronous playback groups. In an example implementation, a first playback device forms a first group with a second playback device. While formed into the first group, the first playback device plays back a first calibration sound contemporaneously with the second playback device. The first playback device forms a second group with a third playback device. While formed into the second group, the first playback device repeatedly plays back a second calibration sound contemporaneously with the third playback device. The first playback device receives data representing (i) first audio processing coefficients and (ii) second audio processing coefficients. The first playback devices applies the first audio processing coefficients to playback of audio content when formed into the first group and the second audio processing coefficients to playback of audio content when formed into the second group.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 120 to, and is acontinuation of, U.S. non-provisional patent application Ser. No.15/909,529, filed on Mar. 1, 2018, entitled “ConcurrentMulti-Loudspeaker Calibration,” which is incorporated herein byreference in its entirety.

U.S. non-provisional patent application Ser. No. 15/909,529 claimspriority under 35 U.S.C. § 120 to, and is a continuation of, U.S.non-provisional patent application Ser. No. 15/478,770, filed on Apr. 4,2017, entitled “Concurrent Multi-Loudspeaker Calibration with a SingleMeasurement,” and issued as U.S. Pat. No. 9,913,057 on Mar. 6, 2018,which is incorporated herein by reference in its entirety.

U.S. non-provisional patent application Ser. No. 15/478,770 claimspriority under 35 U.S.C. § 120 to, and is a continuation of, U.S.non-provisional patent application Ser. No. 14/805,340, filed on Jul.21, 2015, entitled “Concurrent Multi-Loudspeaker Calibration with aSingle Measurement,” and issued as U.S. Pat. No. 9,648,422 on May 9,2017, which is also incorporated herein by reference in its entirety.

This application is related to U.S. patent application Ser. No.13/536,493 filed Jun. 28, 2012, entitled “System and Method for DevicePlayback Calibration,” and U.S. patent application Ser. No. 14/805,140filed Jul. 21, 2015, entitled “Hybrid Test Tone for Space Averaged RoomAudio Calibration Using A Moving Microphone,” which are bothincorporated herein in their entirety.

FIELD OF THE DISCLOSURE

The disclosure is related to consumer goods and, more particularly, tomethods, systems, products, features, services, and other elementsdirected to media playback or some aspect thereof.

BACKGROUND

Options for accessing and listening to digital audio in an out-loudsetting were limited until in 2003, when SONOS, Inc. filed for one ofits first patent applications, entitled “Method for Synchronizing AudioPlayback between Multiple Networked Devices,” and began offering a mediaplayback system for sale in 2005. The Sonos Wireless HiFi System enablespeople to experience music from many sources via one or more networkedplayback devices. Through a software control application installed on asmartphone, tablet, or computer, one can play what he or she wants inany room that has a networked playback device. Additionally, using thecontroller, for example, different songs can be streamed to each roomwith a playback device, rooms can be grouped together for synchronousplayback, or the same song can be heard in all rooms synchronously.

Given the ever growing interest in digital media, there continues to bea need to develop consumer-accessible technologies to further enhancethe listening experience.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, aspects, and advantages of the presently disclosed technologymay be better understood with regard to the following description,appended claims, and accompanying drawings where:

FIG. 1 shows an example media playback system configuration in whichcertain embodiments may be practiced;

FIG. 2 shows a functional block diagram of an example playback device;

FIG. 3 shows a functional block diagram of an example control device;

FIG. 4 shows an example controller interface;

FIG. 5 shows an example flow diagram to facilitate the calibration of aplayback device by causing the playback device to emit a calibrationsound;

FIG. 6 shows a smartphone that is displaying an example controlinterface, according to an example implementation;

FIG. 7 illustrates an example movement through an example environment inwhich an example media playback system is positioned;

FIG. 8 illustrates an example chirp that increases in frequency overtime;

FIG. 9 shows an example brown noise spectrum;

FIGS. 10A and 10B illustrate transition frequency ranges of examplehybrid calibration sounds;

FIG. 11 shows a frame illustrating an iteration of an example periodiccalibration sound;

FIG. 12 shows a series of frames illustrating iterations of an exampleperiodic calibration sound;

FIG. 13 illustrates an example technique to analyze a detectedcalibration sound;

FIG. 14 shows an example flow diagram to facilitate the calibration ofmultiple playback devices by causing the playback devices to emit asequence of calibration sounds;

FIG. 15 illustrates example calibration sounds as might be emitted byrespective playback channels; and

FIG. 16 shows an example flow diagram to emit a calibration sound.

The drawings are for the purpose of illustrating example embodiments,but it is understood that the inventions are not limited to thearrangements and instrumentality shown in the drawings.

DETAILED DESCRIPTION I. Overview

Embodiments described herein involve, inter alia, techniques tofacilitate calibration of a media playback system. Some calibrationprocedures contemplated herein involve a control device of the mediaplayback system detecting and analyzing sound waves (e.g., one or morecalibration sounds) which were emitted by one or more playback devicesof the media playback system. In some examples, such a control devicemay instruct the one or more playback devices to emit a particularcalibration sound that facilitates analysis and calibration.

As indicated above, example calibration procedures may involve aplayback device emitting a calibration sound, which is detected andanalyzed by a control device. In some embodiments, the control devicemay analyze the calibration sound over a range of frequencies over whichthe playback device is to be calibrated (i.e., a calibration range).Accordingly, the particular calibration sound that is emitted by aplayback device covers the calibration frequency range. The calibrationfrequency range may include a range of frequencies that the playbackdevice is capable of emitting (e.g., 15-30,000 Hz) and may be inclusiveof frequencies that are considered to be in the range of human hearing(e.g., 20-20,000 Hz). By emitting and subsequently detecting acalibration sound covering such a range of frequencies, a frequencyresponse that is inclusive of that range may be determined for theplayback device. Such a frequency response may be representative of theenvironment in which the playback device emitted the calibration sound.

Acoustics of an environment may vary from location to location withinthe environment. Because of this variation, some calibration proceduresmay be improved by positioning the playback device to be calibratedwithin the environment as the playback device will later be operated. Inthat position, the environment may affect the calibration sound emittedby a playback device in a similar manner as playback will be affected bythe environment during operation. A set-up phase of a calibrationprocedure may involve positioning the playback device in this position.

Some example calibration procedures may involve detecting thecalibration sound at multiple physical locations within the environment,which may assist in capturing acoustic variability within theenvironment. To facilitate detecting the calibration sound at multiplepoints within an environment, some calibration procedures involve amoving microphone. For example, the microphone that is detecting thecalibration sound may be continuously moved through the environmentwhile the calibration sound is emitted. Such continuous movement mayfacilitate detecting the calibration sounds at multiple physicallocations within the environment, which may provide a betterunderstanding of the environment as a whole.

In some embodiments, a playback device may repeatedly emit thecalibration sound during the calibration procedure such that thecalibration sound covers the calibration frequency range during eachrepetition. With a moving microphone, repetitions of the calibrationsound are continuously detected at different physical locations withinthe environment. For instance, the playback device might emit a periodiccalibration sound. Each period of the calibration sound may be detectedby the control device at a different physical location within theenvironment thereby providing a sample at that location. Such acalibration sound may therefore facilitate a space-averaged calibrationof the environment.

Example calibration sounds may cover the calibration frequency rangeusing various waveforms. Some example calibration procedures mayimplement noise (e.g., pseudorandom periodic noise) that varies over thecalibration frequency range during each period. However, phasedistortion caused by the microphone's movement may make correlating adetected noise signal to the emitted noise signal difficult orimpossible. Other example calibration procedures may implement a sweptsignal (e.g., a swept-sine or chirp) that ascends or descends throughthe frequency range in a pre-determined pattern. A swept signalfacilitates correlating the detected signal to the emitted signal, asthe phase shift is predictable (as Doppler shift). However, at lowerfrequencies, a swept signal may overload the speaker drivers in anattempt to ensure sufficient energy to overcome background noisetypically present in a given environment.

Some example calibration procedures described herein may implement ahybrid calibration sound that includes both noise and a swept signal,which may counter some of these issues. For instance, a hybridcalibration sound may include a noise component that covers lowfrequencies up to a first threshold (e.g., a threshold in the range of50-100 Hz). Such a noise component may be emitted by a playback devicewith sufficient energy to overcome typical background noise (e.g., thatof a quiet room) with a lower risk of overloading the speaker driver(s)of that playback device. The hybrid calibration sound may also include aswept signal (e.g., a swept-sine) that ascends or descends from a secondthreshold up to the highest frequencies of the calibration range (orabove). A predictable signal, like a swept signal, facilitates thecontrol device reversing phase distortion resulting from the microphonemotion.

Since portions of the calibration frequency range may be audible tohumans, some aspects of the calibration sound may be designed to makethe calibration sound more pleasant to a human listener. For instance,some implementations of a hybrid calibration sound may include atransition frequency range in which the noise component and the sweptcomponent overlap. Overlapping these components may avoid possiblyunpleasant sounds that are associated with a harsh transition betweenthe two types of sounds. As another technique to make the calibrationsound more pleasant, the swept portion of the calibration sound maydescend (rather than ascend) through the calibration range. While eitheran ascending or descending swept sine may be effective for calibration,a descending signal may be more pleasant to hear because of theparticular shape of the human ear canal.

In some circumstances, multiple playback devices may be calibratedduring a calibration procedure. For instance, an example calibrationprocedure may calibrate a grouping of playback devices. Such a groupingmight be a zone of a media playback system that includes multipleplayback devices, or, perhaps a grouping might be formed from multiplezones of a media playback system that are grouped into a zone group thatincludes a respective playback device from each zone. Such groupingsmight be physically located within the same environment (e.g., a room ofa house or other building).

In some embodiments, certain portions of the calibration procedure maybe performed concurrently. For instance, multiple playback devices mayemit a calibration sound concurrently. However, when two playbackdevices emit the same portion of the calibration sound concurrently, theconcurrently emitted calibration sounds may interfere with one another,which may prevent the control device from obtaining a measurement ofsufficient quality. Further, the control device might not be able tocorrelate a particular calibration tone to the playback device thatemitted that tone because the same frequency tones areindistinguishable.

With example implementations, the calibration sounds may be tailored inan attempt to avoid such interference. For instance, a baselinecalibration sound that covers the calibration frequency range (i.e., acalibration sound used to calibrate a single playback device) may belengthened such that its duration is proportional to the number ofchannels to be calibrated. For instance, the calibration sound emittedduring the calibration of three channels may be equal in duration tothree multiples of the duration of the baseline calibration sound. Suchstretching may provide sufficient time in each repetition for thechannels to emit a respective calibration sound that covers thecalibration frequency range without overlapping frequencies.

Further, the channels that are emitting the calibration sound may beoffset (i.e., delayed) relative to one another so as to stagger thecalibration sounds. Staggering the calibration sounds may prevent thechannels from outputting the same portion of the calibration sound atthe same time. As noted above, by emitting calibration sounds withoverlapping frequencies, two playback devices can interfere with thecontrol device detecting respective calibration sounds from each device.

Example techniques may involve emitting a hybrid calibration sound. Inone aspect, a method is provided. The method may involve receiving, viaa network interface, a command that instructs the playback device toemit a calibration sound and responsively causing the one or morespeakers to emit a periodic calibration sound that covers a calibrationfrequency range, where the periodic calibration sound comprises (i) afirst component that includes noise at frequencies between a minimum ofthe calibration frequency range and a first threshold frequency, and(ii) a second component that sweeps through frequencies between a secondthreshold frequency and a maximum of the calibration frequency range.

In another aspect, a device is provided. The device includes a networkinterface, at least one processor, a data storage, and program logicstored in the data storage and executable by the at least one processorto perform operations. The operations may include receiving, via thenetwork interface, a command that instructs the playback device to emita calibration sound and responsively causing the one or more speakers toemit a periodic calibration sound that covers a calibration frequencyrange, where the periodic calibration sound comprises (i) a firstcomponent that includes noise at frequencies between a minimum of thecalibration frequency range and a first threshold frequency, and (ii) asecond component that sweeps through frequencies between a secondthreshold frequency and a maximum of the calibration frequency range.

In yet another aspect, a non-transitory computer readable memory isprovided. The non-transitory computer readable memory has stored thereoninstructions executable by a computing device to cause the computingdevice to perform operations. The operations may include receiving, viathe network interface, a command that instructs the playback device toemit a calibration sound and responsively causing the one or morespeakers to emit a periodic calibration sound that covers a calibrationfrequency range, where the periodic calibration sound comprises (i) afirst component that includes noise at frequencies between a minimum ofthe calibration frequency range and a first threshold frequency, and(ii) a second component that sweeps through frequencies between a secondthreshold frequency and a maximum of the calibration frequency range.

Further example techniques may involve multiple playback devicesemitting a calibration sound. In one aspect, a method is provided. Themethod may involve detecting a trigger condition that initiatescalibration of a plurality of playback devices. The method may alsoinvolve sending, to a first playback device of the plurality, a commandthat instructs the first playback device to repeatedly emit acalibration sound according to a sequence, where the calibration soundcycles through frequencies of a calibration frequency range, and where aduration of the calibration sound is proportional to the given number ofplayback devices in the plurality. The method may further involvesending, to one or more additional playback devices of the plurality,respective commands that instruct the one or more additional playbackdevices to repeatedly emit the respective calibration sound according tothe sequence, where the commands instruct the one or more additionalplayback devices to stagger emission of the calibration sounds such thateach emitted calibration sound is delayed relative to a precedingcalibration sound in the sequence. The method may also involvedetecting, via a microphone, the emitted calibration sounds.

In another aspect, a device is provided. The device includes a networkinterface, at least one processor, a data storage, and program logicstored in the data storage and executable by the at least one processorto perform operations. The operations may include detecting a triggercondition that initiates calibration of a plurality of playback devices.The operations may also include sending, to a first playback device ofthe plurality, a command that instructs the first playback device torepeatedly emit a calibration sound according to a sequence, where thecalibration sound cycles through frequencies of a calibration frequencyrange, and where a duration of the calibration sound is proportional tothe given number of playback devices in the plurality. The operationsmay further include sending, to one or more additional playback devicesof the plurality, respective commands that instruct the one or moreadditional playback devices to repeatedly emit the respectivecalibration sound according to the sequence, where the commands instructthe one or more additional playback devices to stagger emission of thecalibration sounds such that each emitted calibration sound is delayedrelative to a preceding calibration sound in the sequence. Theoperations may also include detecting, via a microphone, the emittedcalibration sounds.

In yet another aspect, a non-transitory computer readable memory isprovided. The non-transitory computer readable memory has stored thereoninstructions executable by a computing device to cause the computingdevice to perform operations. The operations may include detecting atrigger condition that initiates calibration of a plurality of playbackdevices. The operations may also include sending, to a first playbackdevice of the plurality, a command that instructs the first playbackdevice to repeatedly emit a calibration sound according to a sequence,where the calibration sound cycles through frequencies of a calibrationfrequency range, and where a duration of the calibration sound isproportional to the given number of playback devices in the plurality.The operations may further include sending, to one or more additionalplayback devices of the plurality, respective commands that instruct theone or more additional playback devices to repeatedly emit therespective calibration sound according to the sequence, where thecommands instruct the one or more additional playback devices to staggeremission of the calibration sounds such that each emitted calibrationsound is delayed relative to a preceding calibration sound in thesequence. The operations may also include detecting, via a microphone,the emitted calibration sounds.

It will be understood by one of ordinary skill in the art that thisdisclosure includes numerous other embodiments. It will be understood byone of ordinary skill in the art that this disclosure includes numerousother embodiments. While some examples described herein may refer tofunctions performed by given actors such as “users” and/or otherentities, it should be understood that this description is for purposesof explanation only. The claims should not be interpreted to requireaction by any such example actor unless explicitly required by thelanguage of the claims themselves.

II. Example Operating Environment

FIG. 1 illustrates an example configuration of a media playback system100 in which one or more embodiments disclosed herein may be practicedor implemented. The media playback system 100 as shown is associatedwith an example home environment having several rooms and spaces, suchas for example, a master bedroom, an office, a dining room, and a livingroom. As shown in the example of FIG. 1, the media playback system 100includes playback devices 102-124, control devices 126 and 128, and awired or wireless network router 130.

Further discussions relating to the different components of the examplemedia playback system 100 and how the different components may interactto provide a user with a media experience may be found in the followingsections. While discussions herein may generally refer to the examplemedia playback system 100, technologies described herein are not limitedto applications within, among other things, the home environment asshown in FIG. 1. For instance, the technologies described herein may beuseful in environments where multi-zone audio may be desired, such as,for example, a commercial setting like a restaurant, mall or airport, avehicle like a sports utility vehicle (SUV), bus or car, a ship or boat,an airplane, and so on.

a. Example Playback Devices

FIG. 2 shows a functional block diagram of an example playback device200 that may be configured to be one or more of the playback devices102-124 of the media playback system 100 of FIG. 1. The playback device200 may include a processor 202, software components 204, memory 206,audio processing components 208, audio amplifier(s) 210, speaker(s) 212,and a network interface 214 including wireless interface(s) 216 andwired interface(s) 218. In one case, the playback device 200 may notinclude the speaker(s) 212, but rather a speaker interface forconnecting the playback device 200 to external speakers. In anothercase, the playback device 200 may include neither the speaker(s) 212 northe audio amplifier(s) 210, but rather an audio interface for connectingthe playback device 200 to an external audio amplifier or audio-visualreceiver.

In one example, the processor 202 may be a clock-driven computingcomponent configured to process input data according to instructionsstored in the memory 206. The memory 206 may be a tangiblecomputer-readable medium configured to store instructions executable bythe processor 202. For instance, the memory 206 may be data storage thatcan be loaded with one or more of the software components 204 executableby the processor 202 to achieve certain functions. In one example, thefunctions may involve the playback device 200 retrieving audio data froman audio source or another playback device. In another example, thefunctions may involve the playback device 200 sending audio data toanother device or playback device on a network. In yet another example,the functions may involve pairing of the playback device 200 with one ormore playback devices to create a multi-channel audio environment.

Certain functions may involve the playback device 200 synchronizingplayback of audio content with one or more other playback devices.During synchronous playback, a listener will preferably not be able toperceive time-delay differences between playback of the audio content bythe playback device 200 and the one or more other playback devices. U.S.Pat. No. 8,234,395 entitled, “System and method for synchronizingoperations among a plurality of independently clocked digital dataprocessing devices,” which is hereby incorporated by reference, providesin more detail some examples for audio playback synchronization amongplayback devices.

The memory 206 may further be configured to store data associated withthe playback device 200, such as one or more zones and/or zone groupsthe playback device 200 is a part of, audio sources accessible by theplayback device 200, or a playback queue that the playback device 200(or some other playback device) may be associated with. The data may bestored as one or more state variables that are periodically updated andused to describe the state of the playback device 200. The memory 206may also include the data associated with the state of the other devicesof the media system, and shared from time to time among the devices sothat one or more of the devices have the most recent data associatedwith the system. Other embodiments are also possible.

The audio processing components 208 may include one or moredigital-to-analog converters (DAC), an audio preprocessing component, anaudio enhancement component or a digital signal processor (DSP), and soon. In one embodiment, one or more of the audio processing components208 may be a subcomponent of the processor 202. In one example, audiocontent may be processed and/or intentionally altered by the audioprocessing components 208 to produce audio signals. The produced audiosignals may then be provided to the audio amplifier(s) 210 foramplification and playback through speaker(s) 212. Particularly, theaudio amplifier(s) 210 may include devices configured to amplify audiosignals to a level for driving one or more of the speakers 212. Thespeaker(s) 212 may include an individual transducer (e.g., a “driver”)or a complete speaker system involving an enclosure with one or moredrivers. A particular driver of the speaker(s) 212 may include, forexample, a subwoofer (e.g., for low frequencies), a mid-range driver(e.g., for middle frequencies), and/or a tweeter (e.g., for highfrequencies). In some cases, each transducer in the one or more speakers212 may be driven by an individual corresponding audio amplifier of theaudio amplifier(s) 210. In addition to producing analog signals forplayback by the playback device 200, the audio processing components 208may be configured to process audio content to be sent to one or moreother playback devices for playback.

Audio content to be processed and/or played back by the playback device200 may be received from an external source, such as via an audioline-in input connection (e.g., an auto-detecting 3.5 mm audio line-inconnection) or the network interface 214.

The network interface 214 may be configured to facilitate a data flowbetween the playback device 200 and one or more other devices on a datanetwork. As such, the playback device 200 may be configured to receiveaudio content over the data network from one or more other playbackdevices in communication with the playback device 200, network deviceswithin a local area network, or audio content sources over a wide areanetwork such as the Internet. In one example, the audio content andother signals transmitted and received by the playback device 200 may betransmitted in the form of digital packet data containing an InternetProtocol (IP)-based source address and IP-based destination addresses.In such a case, the network interface 214 may be configured to parse thedigital packet data such that the data destined for the playback device200 is properly received and processed by the playback device 200.

As shown, the network interface 214 may include wireless interface(s)216 and wired interface(s) 218. The wireless interface(s) 216 mayprovide network interface functions for the playback device 200 towirelessly communicate with other devices (e.g., other playbackdevice(s), speaker(s), receiver(s), network device(s), control device(s)within a data network the playback device 200 is associated with) inaccordance with a communication protocol (e.g., any wireless standardincluding IEEE 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, 802.15, 4Gmobile communication standard, and so on). The wired interface(s) 218may provide network interface functions for the playback device 200 tocommunicate over a wired connection with other devices in accordancewith a communication protocol (e.g., IEEE 802.3). While the networkinterface 214 shown in FIG. 2 includes both wireless interface(s) 216and wired interface(s) 218, the network interface 214 may in someembodiments include only wireless interface(s) or only wiredinterface(s).

In one example, the playback device 200 and one other playback devicemay be paired to play two separate audio components of audio content.For instance, playback device 200 may be configured to play a leftchannel audio component, while the other playback device may beconfigured to play a right channel audio component, thereby producing orenhancing a stereo effect of the audio content. The paired playbackdevices (also referred to as “bonded playback devices”) may further playaudio content in synchrony with other playback devices.

In another example, the playback device 200 may be sonicallyconsolidated with one or more other playback devices to form a single,consolidated playback device. A consolidated playback device may beconfigured to process and reproduce sound differently than anunconsolidated playback device or playback devices that are paired,because a consolidated playback device may have additional speakerdrivers through which audio content may be rendered. For instance, ifthe playback device 200 is a playback device designed to render lowfrequency range audio content (i.e. a subwoofer), the playback device200 may be consolidated with a playback device designed to render fullfrequency range audio content. In such a case, the full frequency rangeplayback device, when consolidated with the low frequency playbackdevice 200, may be configured to render only the mid and high frequencycomponents of audio content, while the low frequency range playbackdevice 200 renders the low frequency component of the audio content. Theconsolidated playback device may further be paired with a singleplayback device or yet another consolidated playback device.

By way of illustration, SONOS, Inc. presently offers (or has offered)for sale certain playback devices including a “PLAY:1,” “PLAY:3,”“PLAY:5,” “PLAYBAR,” “CONNECT:AMP,” “CONNECT,” and “SUB.” Any otherpast, present, and/or future playback devices may additionally oralternatively be used to implement the playback devices of exampleembodiments disclosed herein. Additionally, it is understood that aplayback device is not limited to the example illustrated in FIG. 2 orto the SONOS product offerings. For example, a playback device mayinclude a wired or wireless headphone. In another example, a playbackdevice may include or interact with a docking station for personalmobile media playback devices. In yet another example, a playback devicemay be integral to another device or component such as a television, alighting fixture, or some other device for indoor or outdoor use.

b. Example Playback Zone Configurations

Referring back to the media playback system 100 of FIG. 1, theenvironment may have one or more playback zones, each with one or moreplayback devices. The media playback system 100 may be established withone or more playback zones, after which one or more zones may be added,or removed to arrive at the example configuration shown in FIG. 1. Eachzone may be given a name according to a different room or space such asan office, bathroom, master bedroom, bedroom, kitchen, dining room,living room, and/or balcony. In one case, a single playback zone mayinclude multiple rooms or spaces. In another case, a single room orspace may include multiple playback zones.

As shown in FIG. 1, the balcony, dining room, kitchen, bathroom, office,and bedroom zones each have one playback device, while the living roomand master bedroom zones each have multiple playback devices. In theliving room zone, playback devices 104, 106, 108, and 110 may beconfigured to play audio content in synchrony as individual playbackdevices, as one or more bonded playback devices, as one or moreconsolidated playback devices, or any combination thereof. Similarly, inthe case of the master bedroom, playback devices 122 and 124 may beconfigured to play audio content in synchrony as individual playbackdevices, as a bonded playback device, or as a consolidated playbackdevice.

In one example, one or more playback zones in the environment of FIG. 1may each be playing different audio content. For instance, the user maybe grilling in the balcony zone and listening to hip hop music beingplayed by the playback device 102 while another user may be preparingfood in the kitchen zone and listening to classical music being playedby the playback device 114. In another example, a playback zone may playthe same audio content in synchrony with another playback zone. Forinstance, the user may be in the office zone where the playback device118 is playing the same rock music that is being playing by playbackdevice 102 in the balcony zone. In such a case, playback devices 102 and118 may be playing the rock music in synchrony such that the user mayseamlessly (or at least substantially seamlessly) enjoy the audiocontent that is being played out-loud while moving between differentplayback zones. Synchronization among playback zones may be achieved ina manner similar to that of synchronization among playback devices, asdescribed in previously referenced U.S. Pat. No. 8,234,395.

As suggested above, the zone configurations of the media playback system100 may be dynamically modified, and in some embodiments, the mediaplayback system 100 supports numerous configurations. For instance, if auser physically moves one or more playback devices to or from a zone,the media playback system 100 may be reconfigured to accommodate thechange(s). For instance, if the user physically moves the playbackdevice 102 from the balcony zone to the office zone, the office zone maynow include both the playback device 118 and the playback device 102.The playback device 102 may be paired or grouped with the office zoneand/or renamed if so desired via a control device such as the controldevices 126 and 128. On the other hand, if the one or more playbackdevices are moved to a particular area in the home environment that isnot already a playback zone, a new playback zone may be created for theparticular area.

Further, different playback zones of the media playback system 100 maybe dynamically combined into zone groups or split up into individualplayback zones. For instance, the dining room zone and the kitchen zone114 may be combined into a zone group for a dinner party such thatplayback devices 112 and 114 may render audio content in synchrony. Onthe other hand, the living room zone may be split into a television zoneincluding playback device 104, and a listening zone including playbackdevices 106, 108, and 110, if the user wishes to listen to music in theliving room space while another user wishes to watch television.

c. Example Control Devices

FIG. 3 shows a functional block diagram of an example control device 300that may be configured to be one or both of the control devices 126 and128 of the media playback system 100. Control device 300 may also bereferred to as a controller 300. As shown, the control device 300 mayinclude a processor 302, memory 304, a network interface 306, and a userinterface 308. In one example, the control device 300 may be a dedicatedcontroller for the media playback system 100. In another example, thecontrol device 300 may be a network device on which media playbacksystem controller application software may be installed, such as forexample, an iPhone™ iPad™ or any other smart phone, tablet or networkdevice (e.g., a networked computer such as a PC or Mac™)

The processor 302 may be configured to perform functions relevant tofacilitating user access, control, and configuration of the mediaplayback system 100. The memory 304 may be configured to storeinstructions executable by the processor 302 to perform those functions.The memory 304 may also be configured to store the media playback systemcontroller application software and other data associated with the mediaplayback system 100 and the user.

In one example, the network interface 306 may be based on an industrystandard (e.g., infrared, radio, wired standards including IEEE 802.3,wireless standards including IEEE 802.11a, 802.11b, 802.11g, 802.11n,802.11ac, 802.15, 4G mobile communication standard, and so on). Thenetwork interface 306 may provide a means for the control device 300 tocommunicate with other devices in the media playback system 100. In oneexample, data and information (e.g., such as a state variable) may becommunicated between control device 300 and other devices via thenetwork interface 306. For instance, playback zone and zone groupconfigurations in the media playback system 100 may be received by thecontrol device 300 from a playback device or another network device, ortransmitted by the control device 300 to another playback device ornetwork device via the network interface 306. In some cases, the othernetwork device may be another control device.

Playback device control commands such as volume control and audioplayback control may also be communicated from the control device 300 toa playback device via the network interface 306. As suggested above,changes to configurations of the media playback system 100 may also beperformed by a user using the control device 300. The configurationchanges may include adding/removing one or more playback devices to/froma zone, adding/removing one or more zones to/from a zone group, forminga bonded or consolidated player, separating one or more playback devicesfrom a bonded or consolidated player, among others. Accordingly, thecontrol device 300 may sometimes be referred to as a controller, whetherthe control device 300 is a dedicated controller or a network device onwhich media playback system controller application software isinstalled.

The user interface 308 of the control device 300 may be configured tofacilitate user access and control of the media playback system 100, byproviding a controller interface such as the controller interface 400shown in FIG. 4. The controller interface 400 includes a playbackcontrol region 410, a playback zone region 420, a playback status region430, a playback queue region 440, and an audio content sources region450. The user interface 400 as shown is just one example of a userinterface that may be provided on a network device such as the controldevice 300 of FIG. 3 (and/or the control devices 126 and 128 of FIG. 1)and accessed by users to control a media playback system such as themedia playback system 100. Other user interfaces of varying formats,styles, and interactive sequences may alternatively be implemented onone or more network devices to provide comparable control access to amedia playback system.

The playback control region 410 may include selectable (e.g., by way oftouch or by using a cursor) icons to cause playback devices in aselected playback zone or zone group to play or pause, fast forward,rewind, skip to next, skip to previous, enter/exit shuffle mode,enter/exit repeat mode, enter/exit cross fade mode. The playback controlregion 410 may also include selectable icons to modify equalizationsettings, and playback volume, among other possibilities.

The playback zone region 420 may include representations of playbackzones within the media playback system 100. In some embodiments, thegraphical representations of playback zones may be selectable to bringup additional selectable icons to manage or configure the playback zonesin the media playback system, such as a creation of bonded zones,creation of zone groups, separation of zone groups, and renaming of zonegroups, among other possibilities.

For example, as shown, a “group” icon may be provided within each of thegraphical representations of playback zones. The “group” icon providedwithin a graphical representation of a particular zone may be selectableto bring up options to select one or more other zones in the mediaplayback system to be grouped with the particular zone. Once grouped,playback devices in the zones that have been grouped with the particularzone will be configured to play audio content in synchrony with theplayback device(s) in the particular zone. Analogously, a “group” iconmay be provided within a graphical representation of a zone group. Inthis case, the “group” icon may be selectable to bring up options todeselect one or more zones in the zone group to be removed from the zonegroup. Other interactions and implementations for grouping andungrouping zones via a user interface such as the user interface 400 arealso possible. The representations of playback zones in the playbackzone region 420 may be dynamically updated as playback zone or zonegroup configurations are modified.

The playback status region 430 may include graphical representations ofaudio content that is presently being played, previously played, orscheduled to play next in the selected playback zone or zone group. Theselected playback zone or zone group may be visually distinguished onthe user interface, such as within the playback zone region 420 and/orthe playback status region 430. The graphical representations mayinclude track title, artist name, album name, album year, track length,and other relevant information that may be useful for the user to knowwhen controlling the media playback system via the user interface 400.

The playback queue region 440 may include graphical representations ofaudio content in a playback queue associated with the selected playbackzone or zone group. In some embodiments, each playback zone or zonegroup may be associated with a playback queue containing informationcorresponding to zero or more audio items for playback by the playbackzone or zone group. For instance, each audio item in the playback queuemay comprise a uniform resource identifier (URI), a uniform resourcelocator (URL) or some other identifier that may be used by a playbackdevice in the playback zone or zone group to find and/or retrieve theaudio item from a local audio content source or a networked audiocontent source, possibly for playback by the playback device.

In one example, a playlist may be added to a playback queue, in whichcase information corresponding to each audio item in the playlist may beadded to the playback queue. In another example, audio items in aplayback queue may be saved as a playlist. In a further example, aplayback queue may be empty, or populated but “not in use” when theplayback zone or zone group is playing continuously streaming audiocontent, such as Internet radio that may continue to play untilotherwise stopped, rather than discrete audio items that have playbackdurations. In an alternative embodiment, a playback queue can includeInternet radio and/or other streaming audio content items and be “inuse” when the playback zone or zone group is playing those items. Otherexamples are also possible.

When playback zones or zone groups are “grouped” or “ungrouped,”playback queues associated with the affected playback zones or zonegroups may be cleared or re-associated. For example, if a first playbackzone including a first playback queue is grouped with a second playbackzone including a second playback queue, the established zone group mayhave an associated playback queue that is initially empty, that containsaudio items from the first playback queue (such as if the secondplayback zone was added to the first playback zone), that contains audioitems from the second playback queue (such as if the first playback zonewas added to the second playback zone), or a combination of audio itemsfrom both the first and second playback queues. Subsequently, if theestablished zone group is ungrouped, the resulting first playback zonemay be re-associated with the previous first playback queue, or beassociated with a new playback queue that is empty or contains audioitems from the playback queue associated with the established zone groupbefore the established zone group was ungrouped. Similarly, theresulting second playback zone may be re-associated with the previoussecond playback queue, or be associated with a new playback queue thatis empty, or contains audio items from the playback queue associatedwith the established zone group before the established zone group wasungrouped. Other examples are also possible.

Referring back to the user interface 400 of FIG. 4, the graphicalrepresentations of audio content in the playback queue region 440 mayinclude track titles, artist names, track lengths, and other relevantinformation associated with the audio content in the playback queue. Inone example, graphical representations of audio content may beselectable to bring up additional selectable icons to manage and/ormanipulate the playback queue and/or audio content represented in theplayback queue. For instance, a represented audio content may be removedfrom the playback queue, moved to a different position within theplayback queue, or selected to be played immediately, or after anycurrently playing audio content, among other possibilities. A playbackqueue associated with a playback zone or zone group may be stored in amemory on one or more playback devices in the playback zone or zonegroup, on a playback device that is not in the playback zone or zonegroup, and/or some other designated device. Playback of such a playbackqueue may involve one or more playback devices playing back media itemsof the queue, perhaps in sequential or random order.

The audio content sources region 450 may include graphicalrepresentations of selectable audio content sources from which audiocontent may be retrieved and played by the selected playback zone orzone group. Discussions pertaining to audio content sources may be foundin the following section.

d. Example Audio Content Sources

As indicated previously, one or more playback devices in a zone or zonegroup may be configured to retrieve for playback audio content (e.g.,according to a corresponding URI or URL for the audio content) from avariety of available audio content sources. In one example, audiocontent may be retrieved by a playback device directly from acorresponding audio content source (e.g., a line-in connection). Inanother example, audio content may be provided to a playback device overa network via one or more other playback devices or network devices.

Example audio content sources may include a memory of one or moreplayback devices in a media playback system such as the media playbacksystem 100 of FIG. 1, local music libraries on one or more networkdevices (such as a control device, a network-enabled personal computer,or a networked-attached storage (NAS), for example), streaming audioservices providing audio content via the Internet (e.g., the cloud), oraudio sources connected to the media playback system via a line-in inputconnection on a playback device or network devise, among otherpossibilities.

In some embodiments, audio content sources may be regularly added orremoved from a media playback system such as the media playback system100 of FIG. 1. In one example, an indexing of audio items may beperformed whenever one or more audio content sources are added, removedor updated. Indexing of audio items may involve scanning foridentifiable audio items in all folders/directory shared over a networkaccessible by playback devices in the media playback system, andgenerating or updating an audio content database containing metadata(e.g., title, artist, album, track length, among others) and otherassociated information, such as a URI or URL for each identifiable audioitem found. Other examples for managing and maintaining audio contentsources may also be possible.

Moving now to several example implementations, implementations 500,1400, and 1600 shown in FIGS. 5, 14 and 16, respectively present exampleembodiments of techniques described herein. These example embodimentsthat can be implemented within an operating environment including, forexample, the media playback system 100 of FIG. 1, one or more of theplayback device 200 of FIG. 2, or one or more of the control device 300of FIG. 3. Further, operations illustrated by way of example as beingperformed by a media playback system can be performed by any suitabledevice, such as a playback device or a control device of a mediaplayback system. Implementations 500, 1400, and 1600 may include one ormore operations, functions, or actions as illustrated by one or more ofblocks shown in FIGS. 5, 14 and 16. Although the blocks are illustratedin sequential order, these blocks may also be performed in parallel,and/or in a different order than those described herein. Also, thevarious blocks may be combined into fewer blocks, divided intoadditional blocks, and/or removed based upon the desired implementation.

In addition, for the implementations disclosed herein, the flowchartsshow functionality and operation of one possible implementation ofpresent embodiments. In this regard, each block may represent a module,a segment, or a portion of program code, which includes one or moreinstructions executable by a processor for implementing specific logicalfunctions or steps in the process. The program code may be stored on anytype of computer readable medium, for example, such as a storage deviceincluding a disk or hard drive. The computer readable medium may includenon-transitory computer readable medium, for example, such ascomputer-readable media that stores data for short periods of time likeregister memory, processor cache, and Random Access Memory (RAM). Thecomputer readable medium may also include non-transitory media, such assecondary or persistent long term storage, like read only memory (ROM),optical or magnetic disks, compact-disc read only memory (CD-ROM), forexample. The computer readable media may also be any other volatile ornon-volatile storage systems. The computer readable medium may beconsidered a computer readable storage medium, for example, or atangible storage device. In addition, for the implementations disclosedherein, each block may represent circuitry that is wired to perform thespecific logical functions in the process.

III. Example Techniques to Facilitate Calibration of a Playback Deviceby Causing a Playback Device to Emit a Hybrid Calibration Sound

As discussed above, embodiments described herein may facilitate thecalibration of one or more playback devices. FIG. 5 illustrates anexample implementation 500 to cause a playback device to emit a hybridcalibration sound.

a. Detect Trigger Condition That Initiates Calibration Of At Least OnePlayback Device

At block 502, implementation 500 involves detecting a trigger conditionthat initiates calibration of at least one playback device. Forinstance, a control device, such as control device 126 of media playbacksystem 100, may detect a trigger condition that causes control device126 to initiate calibration of a playback device (e.g., one of playbackdevices 102-124). Alternatively, a playback device of a media playbacksystem may detect such a trigger condition (and perhaps relay anindication of that trigger condition to a control device). As notedabove, calibration of a playback device may involve adjusting one ormore acoustic parameters of a playback device's speakers (i.e.,channels) in an attempt to improve acoustic characteristic of thosespeakers within a given environment.

In some embodiments, detecting the trigger condition may involvedetecting input data indicating a selection of a selectable control. Forinstance, a control device, such as control device 126, may display aninterface (e.g., control interface 400 of FIG. 4), which includes one ormore controls that, when selected, initiate calibration of a playbackdevice, or a group of playback devices (e.g., a zone).

To illustrate such a control, FIG. 6 shows a control device 600 (e.g., asmartphone) which is displaying an example control interface 602.Control interface 602 includes a graphical region 604 that prompts totap selectable control 606 (Start) when ready. When selected, selectablecontrol 606 may initiate the calibration procedure. As shown, selectablecontrol 606 is a button control. While a button control is shown by wayof example, other types of controls are contemplated as well.

Control interface 602 further includes a graphical region 608 thatincludes a video depicting how to assist in the calibration procedure.Some calibration procedures may involve moving a microphone through anenvironment in order to obtain samples of the calibration sound atmultiple physical locations. In order to prompt a user to move themicrophone, the control device may display a video or animationdepicting the step or steps to be performed during the calibration.

To illustrate movement of the control device during calibration, FIG. 7shows media playback system 100 of FIG. 1. FIG. 7 shows a path 700 alongwhich a control device (e.g., control device 126) might be moved duringcalibration. As noted above, the control device may indicate how toperform such a movement in various ways, such as by way of a video oranimation, among other examples.

In other examples, detecting the trigger condition may involve aplayback device detecting that the playback device has becomeuncalibrated, which might be caused by moving the playback device to adifferent position. For example, the playback device may detect physicalmovement via one or more sensors that are sensitive to movement (e.g.,an accelerometer). As another example, the playback device may detectthat it has been moved to a different zone (e.g., from a “Kitchen” zoneto a “Living Room” zone), perhaps by receiving an instruction from acontrol device that causes the playback device to leave a first zone andjoin a second zone.

In further examples, detecting the trigger condition may involve adevice (e.g., a control device or playback device) detecting a newplayback device in the system. Such a playback device may have not yetbeen calibrated for the environment. For instance, a control device maydetect a new playback device as part of a set-up procedure for a mediaplayback system (e.g., a procedure to configure one or more playbackdevices into a media playback system). In other cases, the controldevice may detect a new playback device by detecting input dataindicating a request to configure the media playback system (e.g., arequest to configure a media playback system with an additional playbackdevice).

b. Send Command that Instructs Playback Device(s) To Emit CalibrationSound

Referring back to FIG. 5, at block 504, implementation 500 involvessending a command that instructs the at least one playback device toemit a calibration sound. For instance, a control device, such ascontrol device 126 of media playback system 100, may send a command thatcauses a playback device (e.g., one of playback devices 102-124) to emita calibration sound. The control device may send the command via anetwork interface (e.g., a wired or wireless network interface). Aplayback device may receive such a command, perhaps via a networkinterface, and responsively emit the calibration sound.

The emitted calibration sound may include frequencies that cover acalibration frequency range. As noted above, a control device mayanalyze the calibration sound over a range of frequencies over which theplayback device is to be calibrated (i.e., a calibration range).Accordingly, the command may instruct the playback device to emit acalibration sound that covers the calibration frequency range. Thecalibration frequency range may include a range of frequencies that theplayback device is capable of emitting (e.g., 15-30,000 Hz) and may beinclusive of frequencies that are considered to be in the range of humanhearing (e.g., 20-20,000 Hz). By emitting a calibration tone coveringsuch a range of frequencies, a frequency response that is inclusive ofthat range may be determined for the playback device.

In some embodiments, a playback device may repeatedly emit thecalibration sound during the calibration procedure such that thecalibration sound covers the calibration frequency range during eachrepetition. With a moving microphone, repetitions of the calibrationsound are detected at different physical locations within theenvironment, thereby providing samples that are spaced throughout theenvironment. In some cases, the calibration sound may be periodiccalibration signal in which each period covers the calibration frequencyrange.

To facilitate determining a frequency response, the calibration soundshould be emitted with sufficient energy at each frequency to overcomebackground noise. To increase the energy at a given frequency, a tone atthat frequency may be emitted for a longer duration. However, bylengthening the period of the calibration sound, the spatial resolutionof the calibration procedure is decreased, as the moving microphonemoves further during each period (assuming a relatively constantvelocity). As another technique to increase the energy at a givenfrequency, a playback device may increase the intensity of the tone.However, in some cases, attempting to emit sufficient energy in a shortamount of time may damage speaker drivers of the playback device.

Some implementations may balance these considerations by instructing theplayback device to emit a calibration sound having a period that isapproximately ⅜th of a second in duration (e.g., in the range of ¼ to 1second in duration). In other words, the calibration sound may repeat ata frequency of 2-4 Hz. Such a duration may be long enough to provide atone of sufficient energy at each frequency to overcome background noisein a typical environment (e.g., a quiet room) but also be short enoughthat spatial resolution is kept in an acceptable range (e.g., less thana few feet assuming normal walking speed).

In some embodiments, the command may instruct the playback device toemit a hybrid calibration sound that combines a first component and asecond component having respective waveforms. For instance, an examplehybrid calibration sound might include a first component that includesnoises at certain frequencies and a second component that sweeps throughother frequencies (e.g., a swept-sine). A noise component may coverrelatively low frequencies of the calibration frequency range (e.g.,10-50 Hz) while the swept signal component covers higher frequencies ofthat range (e.g., above 50 Hz). Such a hybrid calibration sound maycombine the advantages of its component signals.

A swept signal (e.g., a chirp or swept sine) is a waveform in which thefrequency increases or decreases with time. Including such a waveform asa component of a hybrid calibration sound may facilitate covering acalibration frequency range, as a swept signal can be chosen thatincreases or decreases through the calibration frequency range (or aportion thereof). For example, a chirp emits each frequency within thechirp for a relatively short time period such that a chirp can moreefficiently cover a calibration range relative to some other waveforms.FIG. 8 shows a graph 800 that illustrates an example chirp. As shown inFIG. 8, the frequency of the waveform increases over time (plotted onthe X-axis) and a tone is emitted at each frequency for a relativelyshort period of time.

However, because each frequency within the chirp is emitted for arelatively short duration of time, the amplitude (or sound intensity) ofthe chirp must be relatively high at low frequencies to overcome typicalbackground noise. Some speakers might not be capable of outputting suchhigh intensity tones without risking damage. Further, such highintensity tones might be unpleasant to humans within audible range ofthe playback device, as might be expected during a calibration procedurethat involves a moving microphone. Accordingly, some embodiments of thecalibration sound might not include a chirp that extends to relativelylow frequencies (e.g., below 50 Hz). Instead, the chirp or swept signalmay cover frequencies between a relatively low threshold frequency(e.g., a frequency around 50-100 Hz) and a maximum of the calibrationfrequency range. The maximum of the calibration range may correspond tothe physical capabilities of the channel(s) emitting the calibrationsound, which might be 20,000 Hz or above.

A swept signal might also facilitate the reversal of phase distortioncaused by the moving microphone. As noted above, a moving microphonecauses phase distortion, which may interfere with determining afrequency response from a detected calibration sound. However, with aswept signal, the phase of each frequency is predictable (as Dopplershift). This predictability facilitates reversing the phase distortionso that a detected calibration sound can be correlated to an emittedcalibration sound during analysis. Such a correlation can be used todetermine the effect of the environment on the calibration sound.

As noted above, a swept signal may increase or decrease frequency overtime. In some embodiments, the control device may instruct the playbackdevice to emit a chirp that descends from the maximum of the calibrationrange (or above) to the threshold frequency (or below). A descendingchirp may be more pleasant to hear to some listeners than an ascendingchirp, due to the physical shape of the human ear canal. While someimplementation may use a descending swept signal, an ascending sweptsignal may also be effective for calibration.

As noted above, example calibration sounds may include a noise componentin addition to a swept signal component. Noise refers to a randomsignal, which is in some cases filtered to have equal energy per octave.In embodiments where the noise component is periodic, the noisecomponent of a hybrid calibration sound might be considered to bepseudorandom. The noise component of the calibration sound may beemitted for substantially the entire period or repetition of thecalibration sound. This causes each frequency covered by the noisecomponent to be emitted for a longer duration, which decreases thesignal intensity typically required to overcome background noise.

Moreover, the noise component may cover a smaller frequency range thanthe chirp component, which may increase the sound energy at eachfrequency within the range. As noted above, a noise component mightcover frequencies between a minimum of the frequency range and athreshold frequency, which might be, for example around a frequencyaround 50-100 Hz. As with the maximum of the calibration range, theminimum of the calibration range may correspond to the physicalcapabilities of the channel(s) emitting the calibration sound, whichmight be 20 Hz or below.

FIG. 9 shows a graph 900 that illustrates an example brown noise. Brownnoise is a type of noise that is based on Brownian motion. In somecases, the playback device may emit a calibration sound that includes abrown noise in its noise component. Brown noise has a “soft” quality,similar to a waterfall or heavy rainfall, which may be consideredpleasant to some listeners. While some embodiments may implement a noisecomponent using brown noise, other embodiments may implement the noisecomponent using other types of noise, such as pink noise or white noise.As shown in FIG. 9, the intensity of the example brown noise decreasesby 6 dB per octave (20 dB per decade).

Some implementations of a hybrid calibration sound may include atransition frequency range in which the noise component and the sweptcomponent overlap. As indicated above, in some examples, the controldevice may instruct the playback device to emit a calibration sound thatincludes a first component (e.g., a noise component) and a secondcomponent (e.g., a sweep signal component). The first component mayinclude noise at frequencies between a minimum of the calibrationfrequency range and a first threshold frequency, and the secondcomponent may sweep through frequencies between a second thresholdfrequency and a maximum of the calibration frequency range.

To overlap these signals, the second threshold frequency may a lowerfrequency than the first threshold frequency. In such a configuration,the transition frequency range includes frequencies between the secondthreshold frequency and the first threshold frequency, which might be,for example, 50-100 Hz. By overlapping these components, the playbackdevice may avoid emitting a possibly unpleasant sound associated with aharsh transition between the two types of sounds.

FIGS. 10A and 10B illustrate components of example hybrid calibrationsignals that cover a calibration frequency range 1000. FIG. 10Aillustrates a first component 1002A (i.e., a noise component) and asecond component 1004A of an example calibration sound. Component 1002Acovers frequencies from a minimum 1008A of the calibration range 1000 toa first threshold frequency 1008A. Component 1004A covers frequenciesfrom a second threshold 1010A to a maximum of the calibration frequencyrange 1000. As shown, the threshold frequency 1008A and the thresholdfrequency 1010A are the same frequency.

FIG. 10B illustrates a first component 1002B (i.e., a noise component)and a second component 1004B of another example calibration sound.Component 1002B covers frequencies from a minimum 1008B of thecalibration range 1000 to a first threshold frequency 1008A. Component1004A covers frequencies from a second threshold 1010B to a maximum1012B of the calibration frequency range 1000. As shown, the thresholdfrequency 1010B is a lower frequency than threshold frequency 1008B suchthat component 1002B and component 1004B overlap in a transitionfrequency range that extends from threshold frequency 1010B to thresholdfrequency 1008B.

FIG. 11 illustrates one example iteration (e.g., a period or cycle) ofan example hybrid calibration sound that is represented as a frame 1100.The frame 1100 includes a swept signal component 1102 and noisecomponent 1104. The swept signal component 1102 is shown as a downwardsloping line to illustrate a swept signal that descends throughfrequencies of the calibration range. The noise component 1104 is shownas a region to illustrate low-frequency noise throughout the frame 1100.As shown, the swept signal component 1102 and the noise componentoverlap in a transition frequency range. The period 1106 of thecalibration sound is approximately ⅜ths of a second (e.g., in a range of¼ to ½ second), which in some implementation is sufficient time to coverthe calibration frequency range of a single channel.

FIG. 12 illustrates an example periodic calibration sound 1200. Fiveiterations (e.g., periods) of hybrid calibration sound 1100 arerepresented as a frames 1202, 1204, 1206, 1208, and 1210. In eachiteration, or frame, the periodic calibration sound 1200 covers acalibration frequency range using two components (e.g., a noisecomponent and a swept signal component).

In some embodiments, a spectral adjustment may be applied to thecalibration sound to give the calibration sound a desired shape, or rolloff, which may avoid overloading speaker drivers. For instance, thecalibration sound may be filtered to roll off at 3 dB per octave, or1/f. Such a spectral adjustment might not be applied to vary lowfrequencies to prevent overloading the speaker drivers.

In some embodiments, the calibration sound may be pre-generated. Such apre-generated calibration sound might be stored on the control device,the playback device, or on a server (e.g., a server that provides acloud service to the media playback system). In some cases, the controldevice or server may send the pre-generated calibration sound to theplayback device via a network interface, which the playback device mayretrieve via a network interface of its own. Alternatively, a controldevice may send the playback device an indication of a source of thecalibration sound (e.g., a URI), which the playback device may use toobtain the calibration sound.

Alternatively, the control device or the playback device may generatethe calibration sound. For instance, for a given calibration range, thecontrol device may generate noise that covers at least frequenciesbetween a minimum of the calibration frequency range and a firstthreshold frequency and a swept sine that covers at least frequenciesbetween a second threshold frequency and a maximum of the calibrationfrequency range. The control device may combine the swept sine and thenoise into the periodic calibration sound by applying a crossover filterfunction. The cross-over filter function may combine a portion of thegenerated noise that includes frequencies below the first thresholdfrequency and a portion of the generated swept sine that includesfrequencies above the second threshold frequency to obtain the desiredcalibration sound. The device generating the calibration sound may havean analog circuit and/or digital signal processor to generate and/orcombine the components of the hybrid calibration sound.

In some embodiments, prior to sending the command that instructs theplayback device to emit the calibration sound, the control device maydetermine whether the ambient noise in the environment exceeds athreshold level, such that the ambient noise might affect thecalibration procedure. The threshold level may be consistent with aquiet room (e.g., 30-50 dB). If the ambient noise exceeds the thresholdsound pressure level, the control device may cause a graphical interfaceto display a request to lower the ambient noise level of the calibrationenvironment. During or after providing such a display, the controldevice may re-test the sound pressure level of the environment todetermine whether ambient noise of the environment has been reduced tobelow the threshold level. While a control device has been described byway of example as testing the ambient sound pressure level, inalternative embodiments the playback device may determine whether theambient noise in the environment exceeds the threshold level andtransmit this status (or the sound pressure level of the environment) tothe control device.

The instruction that causes the playback device to emit the calibrationsound may include (or be accompanied by in a separate transmission)parameters that influence the calibration procedure. For instance, thecontrol device may send an indication of the type of microphone (or thetype of control device, which may indicate the type of microphone) tothe playback device. The microphone that is ultimately used to detectthe calibration sound may have a response of its own, which mayinfluence how the calibration sound is perceived. For instance, a givenmicrophone might be sensitive to frequencies between 10 Hz and 22,000Hz, such that any portion(s) of the calibration sound which are outsideof this range are unable to be detected by the microphone. As anotherexample, a particular microphone might be more or less sensitive tocertain frequencies, such that certain frequencies may be detected bythe microphone as relatively louder or quieter. Some calibrationprocedures may be improved by offsetting such characteristics of themicrophone.

Another parameter that may influence the calibration procedure is theroom size, as playback device may emit the calibration sound at a volumethat is proportional to the room size. For instance, when receiving anindication that the calibration environment is a relatively large room,the playback device may emit the calibration sound with at a firstvolume level (which is a relatively high sound pressure level).Conversely, when receiving an indication that the calibrationenvironment is a relatively small room, the playback device may emit thecalibration sound with at a second volume level that is a lower soundpressure level than the first volume level. A higher sound pressurelevel may facilitate the calibration sound propagating through a largeenvironment and reflecting back to the microphone with sufficientintensity to be detectable over ambient noise.

The calibration sound may also be based on the type of playback device.Some playback devices may emit sounds at certain frequencies with moreor less intensity than other frequencies. For instance, a playbackdevice with a tweeter may emit high frequencies at a higher intensitythan a playback device without a tweeter. Further, such a playbackdevice might be capable of outputting higher frequencies than a playbackdevice without a tweeter. Accordingly, in some embodiments, the playbackdevice may adjust the calibration sound to increase or decrease thesound intensity at certain frequencies, or might determine a particularcalibration range based on the type of playback device (and itscapabilities).

c. Detect Emitted Calibration Sound(s)

In FIG. 5, at block 506, implementation 500 involves detecting theemitted calibration sound. For instance, a control device, such ascontrol device 126 of media playback system 100, may detect, via amicrophone, at least a portion of the emitted calibration sound. Giventhat the microphone is moving throughout the calibration environment,the control device may detect iterations of the calibration sound atdifferent physical locations of the environment, which may provide abetter understanding of the environment as a whole.

For example, referring back to FIG. 7, control device 126 may detectcalibration sounds emitted by a playback device (e.g., playback device108) at various points along the path 700 (e.g., at point 702 and/orpoint 704). Alternatively, the control device may record the calibrationsignal along the path. In some embodiments, the playback device may playa periodic calibration signal (or perhaps repeat the same calibrationsignal) such that the playback device records an instance of thecalibration signal at different points along the paths. Comparison ofsuch recordings may indicate how the acoustic characteristics changefrom one physical location in the environment to another, whichinfluences the calibration settings chosen for the playback device inthat environment.

After the control device records the calibration sounds, the recordingsof the calibration sounds may be analyzed to determine calibrationsettings for the playback device. In some embodiments, the controldevice may analyze the calibration sounds itself Alternatively, thecontrol device may transmit the recordings (or a portion thereof) toanother computing system (perhaps a computing system with moreprocessing power, such as a personal computer or server (e.g., a serverinvolved in providing a cloud computing service).

FIG. 13 illustrates an example implementation 1300 of a technique toanalyze a detected calibration sound. At block 1302, a control devicedetects calibration sounds, perhaps using the techniques discussed inconnection with block 506 of FIG. 6. At block 1304, one or moreprocessors (e.g., processor(s) 202 of control device 200 illustrated inFIG. 2) receive the detected calibration sounds as an input. At block1306, the one or more processors identify frames (e.g., periods) of thecalibration sound, such as frames 1202 through 1210 of FIG. 12. Asdiscussed above, individual frames may include a repetition of thecalibration sound such that the frame includes a detect sound thatcovers frequencies across a calibration frequency range.

At block 1308, the one or more processors correct for characteristics ofthe microphone used to detect the calibration sound. To facilitate suchcorrection, at block 1310, the one or more processors receive amicrophone correction curve that indicates the frequency response of themicrophone. Using such a curve, the one or more processors can offseteffects of the particular microphone on the detected calibration sound.

At block 1312, the one or more processors determine whether each thedetected calibration sound in each frame satisfies a threshold signal tonoise ratio. Detected calibration sounds that do not satisfy thisthreshold may be excluded from the analysis, as ambient noise may haveinterfered with the emission and detection of these instances of thecalibration sound.

At block 1314, the one or more processors average the response curves ofthe detected calibration sounds. As noted above, with a movingmicrophone, repetitions of the calibration sound are detected atdifferent physical locations within the environment, thereby providingsamples that are spaced throughout the environment. By averagingmultiple response curves from different locations within theenvironment, the one or more processors may determine a responseindicative of the environment as a whole.

At block 1316, the one or more processors may receive a targetcalibration. In some embodiments, the target calibration may be a flatresponse (i.e., a calibration that treats different frequenciesequally). In other embodiments, the target calibration may emphasizecertain frequencies and de-emphasize others. For instance, the targetcalibration may emphasis bass and treble frequencies.

At block 1318, the one or more processors generate an offset curve basedon the averaged response and the target calibration. In particular, theone or more processors may determine a offset curve that achieves thetarget calibration by offsetting the averaged responses of theenvironment.

At block 1320, the one or more processors determine a calibrationprofile. Such a calibration profile may include one or more coefficientsto apply to the playback device, to cause the calibration device tooffset the response of the environment. At block 1322, the calibrationprofile is transmitted to the playback device, which may adopt thecalibration profile.

Some further example techniques for analyzing such recordings aredescribed in U.S. patent application Ser. No. 13/536,493 filed Jun. 28,2012, entitled “System and Method for Device Playback Calibration,” U.S.patent application Ser. No. 14/216,306 filed Mar. 17, 2014, entitled“Audio Settings Based On Environment,” and U.S. patent application Ser.No. 14/481,511 filed Sep. 9, 2014, entitled “Playback DeviceCalibration,” which are incorporated herein in their entirety.

IV. Example Techniques to Facilitate Calibration of Multiple PlaybackDevices

As discussed above, embodiments described herein may facilitate thecalibration of multiple playback devices by causing the playback devicesto emit a sequence of calibration sounds. FIG. 14 illustrates an exampleimplementation 1400 to cause multiple playback devices to emitcalibration sounds in sequence.

a. Detect Trigger Condition That Initiates Calibration Of MultiplePlayback Channels

At block 1402, implementation 1400 involves detecting a triggercondition that initiates calibration of multiple playback channels. Forinstance, a control device, such as control device 126 shown in FIG. 1,may detect a trigger condition that causes control device 126 toinitiate calibration of two or more playback channels (e.g., two or morespeakers of a single playback device such as one of playback devices102-124 or possibly two or more of playback devices 102-124).Alternatively, a playback device of a media playback system (e.g., mediaplayback system 100) may detect such a trigger condition (and perhapsrelay an indication of that trigger condition to a control device).Calibration of multiple playback devices may involve the multipleplayback devices emitting a respective calibration sound according to asequence. After detecting these emitted calibration sounds, the detectedcalibration sounds may be analyzed so as to determine how one or morerespective acoustic parameters of the playback device's speakers can beadjusted in an attempt to improve acoustic characteristic of thosespeakers within the calibration environment.

As noted above, a trigger condition may initiate calibration of multipleplayback channels. A given playback device may include multiplespeakers. In some embodiments, these multiple channels may be calibratedindividually as respective channels. Alternatively, the multiplespeakers of a playback device may be calibrated together as one channel.In further cases, groups of two or more speakers may be calibratedtogether as respective channels. For instance, some playback devices,such as sound bars intended for use with surround sound systems, mayhave groupings of speakers designed to operate as respective channels ofa surround sound system. Each grouping of speakers may be calibratedtogether as one playback channel (or each speaker may be calibratedindividually as a separate channel).

In some embodiments, detecting the trigger condition may involvedetecting a trigger condition that initiates calibration of a particularzone. As noted above in connection with the example operatingenvironment, playback devices of a media playback system may be joinedinto a zone in which the playback devices of that zone operate jointlyin carrying out playback functions. For instance, two playback devicesmay be joined into a bonded zone as respective channels of a stereopair. Alternatively, multiple playback devices may be joined into a zoneas respective channels of a surround sound system. Some example triggerconditions may initiate a calibration procedure that involvescalibrating the playback devices of a zone. As noted above, withinvarious implementations, a playback device with multiple speakers may betreated as a mono playback channel or each speaker may be treated as itsown channel, among other examples.

In further embodiments, detecting the trigger condition may involvedetecting a trigger condition that initiates calibration of a particularzone group. Two or more zones, each including one or more respectiveplayback devices, may be joined into a zone group of playback devicesthat are configured to play back media in synchrony. In some cases, atrigger condition may initiate calibration of a given device that ispart of such a zone group, which may initiate calibration of theplayback devices of the zone group (including the given device).Alternatively,

Various types of trigger conditions may initiate the calibration of themultiple playback devices. In some embodiments, detecting the triggercondition involves detecting input data indicating a selection of aselectable control. For instance, a control device, such as controldevice 126, may display an interface (e.g., control interface 600 ofFIG. 6), which includes one or more controls that, when selected,initiate calibration of a playback device, or a group of playbackdevices (e.g., a zone). Alternatively, detecting the trigger conditionmay involve a playback device detecting that the playback device hasbecome uncalibrated, which might be caused by moving the playback deviceto a different position or location within the calibration environment.For instance, an example trigger condition might be that a physicalmovement of one or more of the plurality of playback devices hasexceeded a threshold magnitude. In further examples, detecting thetrigger condition may involve a device (e.g., a control device orplayback device) detecting a change in configuration of the mediaplayback system, such as a new playback device being added to thesystem. Other examples are possible as well.

b. Send Command that Instructs Playback Device(s) To Emit CalibrationSound

Referring back to FIG. 14, at block 1404, implementation 1400 involvessending a command that instructs the multiple playback devices to emitrespective calibration sounds. For instance, a control device, such ascontrol device 126 of media playback system 100, may send respectivecommands that cause two or more playback devices (e.g., two or more ofplayback devices 102-124) to emit a calibration sound. The controldevice may send the commands via a network interface (e.g., a wired orwireless network interface). Upon receiving such a command, eachplayback device may responsively emit a calibration sound.

The command may instruct the multiple playback devices to emit thecalibration sounds according to a sequence. The sequence may govern theorder in which the playback devices emit the calibration sound. Forexample, the commands may instruct a first playback device to emit thecalibration sound first in the sequence, a second playback device toemit the calibration sound second in the sequence, a third playbackdevice to emit the calibration sound third in the sequence, and so onfor the given number of playback channels to be calibrated during agiven calibration procedure.

As described above in connection with some example techniques, acalibration sound may include frequencies that cover the calibrationfrequency range. As noted above, some example calibration frequencyranges may include frequencies that the speaker(s) of a given playbackchannel is capable of emitting, or perhaps frequencies over which thecalibration procedure is intended to calibrate the channel. Examplecalibration ranges may be inclusive of the range of 20-20,000 Hz, whichis generally considered to be the range of human hearing. Examplecalibration sound may cover this range using a variety of waveforms. Forinstance, upward, downward, or oscillating swept-sine or chirp tones maycover such a frequency range by varying frequency over time. Random orpseudorandom noise may cover a calibration frequency range. Some musicalcompositions (e.g., songs) may cover the calibration frequency range.

In some embodiments, the playback devices may emit a hybrid calibrationsound, such as the example hybrid calibration sound discussed above. Forinstance, each playback device may emit a calibration sound thatincludes a noise component and a swept signal component. The noisecomponent may cover low frequencies of a calibration range (e.g., arange inclusive of a minimum of the calibration frequency range to afirst threshold) while the swept signal component covers higherfrequencies (e.g., the higher frequencies of the calibration not coveredby the noise component). In some cases, component of a hybridcalibration sound may overlap in a transition frequency range, which mayhave various benefits, such as a more pleasant sound.

Alternatively, each playback devices may emit two or more sounds duringeach iteration (or period). Like components of a hybrid calibrationsound, each sound may cover different portions of a calibrationfrequency range (with possibly some overlap). For instance, a firstsound may include low frequency noise (e.g., noise at frequencies belowa certain threshold). A second sound may include higher frequencies, soas to cover a calibration frequency range in combination with the firstsound. The second sound may cover higher frequencies of the frequencyrange using a variety of waveforms such as a sine-sweep or chirp tone,or possibly a different type of noise, among other examples.

Using different waveforms may affect the minimum duration of each cycleor repetition of the calibration sound. Some calibration proceduresrequire at least a minimum amount of sound energy to be emitted at eachfrequency of the calibration range to overcome background noise. Auniform signal may cover a calibration frequency range more quickly byproceeding through the frequencies of the range in an orderly manner.For example, a swept signal may efficiently cover a calibrationfrequency range by varying frequency at a rate that emits sufficientenergy at each frequency. In contrast, less uniform signals might causeinsufficient energy to be emitted at some frequencies (and perhapsexcessive energy at other frequencies). For example, a hip hop song thatis heavy on bass and light on treble may repeat certain bass frequenciesoften which may cause excessive energy to be emitted at thosefrequencies and not enough energy at treble frequencies, which mayresult in the song being emitted for a longer duration in order to coverthe calibration frequency range with sufficient energy at eachfrequency.

A shorter duration of each cycle or repetition of the calibration soundmay improve the spatial resolution of the calibration procedure.Assuming a moving microphone at substantially constant velocity, acalibration sound that has a shorter period will result in samples thatare closer together within the calibration environment (i.e., withhigher spatial resolution). As noted above, for a single playbackchannel, a sound that is approximately ⅜th of a second in length is longenough to cover a calibration frequency range with sufficient energy ateach frequency while maintain good spatial resolution. However, whencalibrating multiple playback channels, each playback channel shouldemit a calibration sound that covers the calibration frequency range.Instructing the multiple playback devices to emit the calibration soundsuccessively may increase the total duration of the calibration soundsto a point where spatial resolution is degraded.

To maintain acceptable spatial resolution when calibrating multipleplayback channels, the command may instruct the multiple playbackdevices to concurrently emit the calibration sound. By emitting thecalibration sounds concurrently, rather than successively, the time (anddistance) between samples may be kept to an acceptable distance (e.g.under a meter). However, concurrently emitted signals may interfere withone another if the same frequencies are emitted at the same time. Forinstance, if two playback channels emit a 1000 Hz tone concurrently, therespective 1000 Hz tones from each channel might not be able to beindependently detected.

To avoid interference, the command may instruct the playback channels tostagger the calibration sounds such that each successive playbackchannel in the sequence emits the calibration sound after a delayrelative to the preceding playback channel in the sequence. Bystaggering the start times of each calibration sound, a first cycle ofcalibration sounds may fully (or partially) overlap without causinginterference, as, at any given point, each playback channel may output adifferent portions calibration frequency range. However, because thecalibration sounds repeat, successive cycles may interfere withpreceding cycles. In an attempt to avoid this possibility, the durationof each period or repetition of the calibration sound may be stretchedin proportion to the number of playback channels to be calibrated.

To illustrate, FIG. 15 shows example hybrid calibration sounds as mightbe emitted during an example calibration procedure of playback channels1502, 1504, 1506, and 1508. The hybrid calibration sounds in FIG. 15 arebased on hybrid calibration sound 1100 of FIG. 11, which can beconsidered a “baseline” tone that is used in the calibration of a singleplayback channel. To avoid overlapping frequencies, the example hybridcalibration sounds are stretched and staggered.

More particularly, playback channels 1502, 1504, 1506, and 1508 staggeroutput of the calibration sound relative to one another. At time t_0,playback channel 1502 begins emitting the calibration sound. After adelay, playback channel 1504 begins emitting the calibration sound.After another delay, playback channel 1506 begins emitting thecalibration sound. Likewise, playback channel 1508 begins emitting thecalibration sound after a delay relative to playback channel 1506. Theamount of delay may vary by implementation. In this example, eachplayback channel delays output of the calibration by one half of theduration of the baseline tone (i.e., ½ of ⅜ths of a second, or 3/16thsof a second). As shown in FIG. 15, this delay produces a staggering ofthe calibration sounds over time, which helps to prevent overlapping offrequencies.

The hybrid calibration sounds in FIG. 15 have been stretched such thatthey have a duration that is four times the duration of the baselinetone (i.e., hybrid calibration sound 1100). This multiple of 4× is equalto the number of playback channels to be calibrated (i.e., channels1502, 1504, 1506, and 1508). By stretching the baseline tone inproportion to the number of channels, there is sufficient time in eachframe for each playback channel to cover the calibration frequency rangewithout overlapping frequencies. As shown in FIG. 15, during each offrames 1510, 1512, 1514, 1418, and 1520, channels 1502, 1504, 1506 and1508 emit respective calibration sounds that cover the calibrationfrequency range. As described above, hybrid calibration sound 1100includes a noise component that covers frequencies of the calibrationfrequency range up to a threshold and a swept signal component thatcovers frequencies of the calibration frequency range down to thethreshold (perhaps with some overlap between the components).

Frames 1510, 1512, 1514, 1418, and 1520 are separated by respectiveguardbands (e.g., guardband 1520) in which no portion of a swept signalis emitted by any of the playback devices. This guardband provides timefor the emitted calibration sounds to propagate through the environmentto the moving microphone before the next iteration of the calibrationsounds begin. By providing this propagation time, the guardband helps toprevent overlapping frequencies, which may interfere with calibration.

In FIG. 15, five iterations of the calibration sound emitted by eachplayback channel are shown by way of example. During example calibrationprocedures, the calibration sound may be repeatedly emitted multipletimes so as to generate samples throughout the environment (given thatthe microphone that is detecting the calibration sound is moving). Forinstance, during some example calibration procedures, the calibrationsounds depicted in FIG. 15 may repeat for a calibration duration of30-45 seconds, thereby generating 20-30 samples (given that thecalibration sounds have a duration of 1.5 seconds, which is equivalentto a baseline duration of ⅜ second multiplied by four channels). Thenumber of repetitions and the duration of the calibration sound may varyby implementation and number of playback channels, which may cause thecalibration duration to vary.

In some embodiments, the calibration sounds emitted by the playbackdevices may be stored as one or more recordings. For instance, a controldevice may store a recording (e.g., a sound file) with multiple channelsperhaps with each of the multiple channels containing a calibrationsound for a different channel (or playback device) to be calibrated. Insome example implementations, the calibration sound emitted by eachplayback channel may be stored as a channel of a multi-channel file(e.g., an Ogg file). Such a recording may pre-stagger the calibrationsounds emitted by each playback channel and pre-stretch the calibrationsounds to a duration that is proportional to the number of playbackchannels to be calibrated, such that by initiating playback of themulti-channel in synchrony on the multiple playback channels, thecalibration sounds emitted by the playback channels device do notoverlap frequencies.

In some cases, the playback devices of the media playback system mightnot have access to recordings with the same number of channels as thenumber of playback channels to be calibrated. For instance, the playbackdevices may only have recordings for 1, 2, 4, or 8 channels (i.e.,powers of two). In such embodiments, a particular recording may beselected based on the number of channels to be calibrated. For instance,to calibrate three channels, the number of channels (3) might be roundedup to the four channel recording, as a four channel recording hassufficient channels to calibrate three playback channels. The fourthchannel may remain unused during the calibration of the three playbackchannels. Likewise, to calibrate five playback channels, a controldevice may instruct the playback channels to emit respective channels ofan eight channel recording.

Such an implementation may reduce the number of recording that aremaintained by a given media playback system, as a recording might notneed to be stored for every possible combination of channels. Whilerecordings with 1, 2, 4, and 8 channels have been described by way ofexample, the respective number of channels in each stored recording mayvary by implementation. For instance, in some cases, three and sixchannel recordings may be stored, as calibrating three channel (e.g.,2.1 stereo with a subwoofer) zones or six channel (e.g., 5.1 surround)zones might be relatively common calibration procedures.

As an alternative to pre-recorded calibration sounds, the calibrationsounds may be mixed or generated as part of the calibration procedure.For instance, a device of the media playback system (e.g., a playbackdevice or a control device) may have access to component tones (e.g.,noise and swept signal components, among other examples) and combinethose components using a crossover filter function or other signalprocessing technique using an analog filter or digital signal processor.In some cases, the device may generate the component tones prior tomixing the tones into calibration sound.

In some embodiments, the calibration sound may be generated and/orstored on a first device (e.g., a control device or remote server) andbe sent to the playback device for playback by one or more playbackchannels during the calibration. Such an approach may provide greaterflexibility in the calibration sounds available to the media playbacksystem. Additionally, this approach may alleviate the need for theplayback device to contain data storage large enough to store thecalibration sound. Further, as another possible benefit, storing thecalibration sound on another device may facilitate updating thecalibration sound with new recordings.

c. Detect Emitted Calibration Sound(s)

In FIG. 14, at block 1406, implementation 1400 involves detecting theemitted calibration sounds. For instance, a control device, such ascontrol device 126 of media playback system 100, may detect, via amicrophone, at least a portion of the emitted calibration sounds. Giventhat the microphone is moving throughout the calibration environment,the control device may detect iterations of the calibration sounds atdifferent physical locations within the environment.

So as to calibrate the individual playback channels, the control devicemay determine which playback channel emitted each particular instance ofthe calibration sound that was detected by the control device. Aftercorrelating each detected calibration sound to the playback channel thatemitted that particular instance of the calibration sound, therecordings of the calibration sounds may be analyzed to determinecalibration settings for the playback device. In some embodiments,analysis of the calibration sounds may involve a device, such as acontrol device or remote server, determining from the identifiedcalibration sounds a respective frequency response of each playbackchannel. After determining such a response, the device may calibrateeach playback device by sending the device a command with calibrationparameters that equalize the determined frequency response to a desiredfrequency response (e.g., a “flat” frequency response).

In some embodiments, a device may identify the detected calibrationsounds by the order in which the calibration sounds were detected. Asnoted above, the command that instructs the multiple playback devices toemit respective calibration sounds may instruct the multiple playbackdevices to emit the calibration sounds according to a sequence thatgoverns the order in which the calibration sounds are emitted. Giventhat sequence is known to the control device, the control device maydetermine which playback channel emitted each particular instance of thecalibration sound by the order in which the calibration sounds weredetected, as that order may be the same as governed by the sequence.

Within examples, the calibration sound emitted by each playback channelmay include a unique “notch.” Such a notch may be a substantial increaseor decrease in amplitude at a particular frequency. Each playbackchannel may emit a calibration sound with a notch at a differentfrequency, which may act as a watermark. For example, the commands sendto the playback devices may instruct a first playback channel to emit acalibration sound with a notch at a first frequency (e.g., 1000 Hz), asecond playback channel to emit a calibration sound with a notch at asecond frequency (e.g., 5000 Hz), and so on for the given number ofplayback channels to be calibrated during a given calibration procedure.Upon detecting the calibration sound with the notch at the firstfrequency, a device may be able to identify that calibration sound asbeing emitted by the first playback channel. Likewise, a notch at thesecond frequency in a detect calibration sound may identify thatcalibration sound as being emitted by the second playback channel. Sucha technique may be used in combination with identifying the calibrationsounds based on the order in which they were emitted and detected, whichmay improve identification reliability.

V. Example Techniques to Emit Calibration Sound(s)

As discussed above, embodiments described herein may facilitate thecalibration of one or more playback devices. FIG. 16 illustrates anexample implementation 1600 that involves a playback device to emittinga hybrid calibration sound, according to an example embodiment.

a. Receive Command that Instructs Playback Device(s) To Emit CalibrationSound(s)

At block 1602, implementation 1600 involves receiving a command thatinstructs a playback device to emit a calibration sound. For instance, aplayback device, such as one of playback devices 102-124, may receive acommand that causes the playback device to emit a calibration sound. Asnoted above, such a command may be sent from a control device (e.g.,control device 126 or control device 128 of media playback system 100).The playback device may receive the command via a network interface(e.g., a wired or wireless network interface).

The command may instruct the playback device to emit a calibration soundthat includes frequencies that cover a calibration frequency range. Asnoted above, a control device may analyze the calibration sound over arange of frequencies over which the playback device is to be calibrated(i.e., a calibration range). Accordingly, the command may instruct theplayback device to emit a calibration sound that covers the calibrationfrequency range. The calibration frequency range may include a range offrequencies that the playback device is capable of emitting (e.g.,15-30,000 Hz) and may be inclusive of frequencies that are considered tobe in the range of human hearing (e.g., 20-20,000 Hz). By emitting acalibration tone covering such a range of frequencies, a frequencyresponse that is inclusive of that range may be determined for theplayback device.

In some embodiments, the playback device may repeatedly emit thecalibration sound during the calibration procedure such that thecalibration sound covers the calibration frequency range during eachrepetition. With a moving microphone, repetitions of the calibrationsound are detected at different physical locations within theenvironment, thereby providing samples that are spaced throughout theenvironment. In some cases, the calibration sound may be periodiccalibration signal in which each period covers the calibration frequencyrange.

As described above, such a command may instruct the playback device toemit a hybrid calibration sound that combines a first component and asecond component having respective waveforms. For example, an examplehybrid calibration sound might include two components: a first componentthat includes noises at certain frequencies and a second component thatsweeps through other frequencies (e.g., a swept-sine). The noisecomponent may cover lower frequencies of the calibration frequency range(e.g., 10-50 Hz) while the swept signal component covers higherfrequencies of that range (e.g., above 50 Hz).

Some implementations of a hybrid calibration sound may include atransition frequency range in which the noise component and the sweptcomponent overlap. As indicated above, in some examples, the controldevice may instruct the playback device to emit a calibration sound thatincludes a first component (e.g., a noise component) and a secondcomponent (e.g., a sweep signal component). The first component mayinclude noise at frequencies between a minimum of the calibrationfrequency range and a first threshold frequency, and the secondcomponent may sweep through frequencies between a second thresholdfrequency and a maximum of the calibration frequency range.

To overlap these signals, the second threshold frequency may a lowerfrequency than the first threshold frequency. In such a configuration,the transition frequency range includes frequencies between the secondthreshold frequency and the first threshold frequency, which might be,for example, 50-100 Hz. By overlapping these components, the playbackdevice may avoid emitting a possibly unpleasant sound associated with aharsh transition between the two types of sounds.

In some embodiments, the calibration sound may be pre-generated. Such apre-generated calibration sound might be stored on the control device,the playback device, or on a server (e.g., a server that provides acloud service to the media playback system). In some cases, the playbackdevice may receive the pre-generated calibration sound from a controldevice via a network interface. Alternatively, a playback device mayreceive an indication of a source of the calibration sound (e.g., aURI), which the playback device may use to obtain the calibration sound.

Alternatively, the playback device may generate the calibration sound.For instance, for a given calibration range, the playback device maygenerate noise that covers at least frequencies between a minimum of thecalibration frequency range and a first threshold frequency and a sweptsine that covers at least frequencies between a second thresholdfrequency and a maximum of the calibration frequency range. The playbackdevice may combine the swept sine and the noise into the periodiccalibration sound by applying a crossover filter function. Thecross-over filter function may combine a portion of the generated noisethat includes frequencies below the first threshold frequency and aportion of the generated swept sine that includes frequencies above thesecond threshold frequency to obtain the desired calibration sound. Theplayback device may have an analog circuit and/or digital signalprocessor to generate and/or combine the components of the hybridcalibration sound.

Within examples, the command may instruct the playback device to emitthe calibration sounds according to a sequence with one or moreadditional playback device. The sequence may govern the order in whichthe playback devices emit the calibration sound. For example, thecommands may instruct a first playback device to emit the calibrationsound first in the sequence, a second playback device to emit thecalibration sound second in the sequence, a third playback device toemit the calibration sound third in the sequence, and so on for thegiven number of playback channels to be calibrated during a givencalibration procedure.

As noted above, a playback device may include multiple speakers. Thesemultiple channels may be calibrated individually as respective channels.Alternatively, the multiple speakers of a playback device may becalibrated as one channel. In further cases, groups of two or morespeakers may be calibrated together as respective channels.

As described above in connection with FIGS. 13 and 14, the command mayinstruct the playback device to stagger the calibration sounds such thateach successive playback channel in the sequence emits the calibrationsound after a delay relative to the preceding playback channel in thesequence. By staggering the start times of each calibration sound, afirst cycle of calibration sounds may fully (or partially) overlapwithout causing interference, as, at any given point, each playbackchannel may output a different portions calibration frequency range.However, because the calibration sounds repeat, successive cycles mayinterfere with preceding cycles. In an attempt to avoid thispossibility, the duration of each period or repetition of thecalibration sound may be stretched in proportion to the number ofplayback channels to be calibrated.

b. Emit Calibration Sound(s)

Referring still to FIG. 16, at block 1604, implementation 1600 involvesemitting a calibration sound. For example, the playback device (e.g.,one of playback devices 102-124), may emit the calibration soundaccording to the received command that causes the playback device toemit the calibration sound. As described above, such a command mayinstruct the playback device to emit a particular calibration soundhaving certain characteristics, perhaps according to a particularsequence.

VI. Conclusion

The description above discloses, among other things, various examplesystems, methods, apparatus, and articles of manufacture including,among other components, firmware and/or software executed on hardware.It is understood that such examples are merely illustrative and shouldnot be considered as limiting. For example, it is contemplated that anyor all of the firmware, hardware, and/or software aspects or componentscan be embodied exclusively in hardware, exclusively in software,exclusively in firmware, or in any combination of hardware, software,and/or firmware. Accordingly, the examples provided are not the onlyway(s) to implement such systems, methods, apparatus, and/or articles ofmanufacture.

Example techniques may involve emitting a hybrid calibration sound. Inone aspect, a method is provided. The method may involve receiving, viaa network interface, a command that instructs the playback device toemit a calibration sound and responsively causing the one or morespeakers to emit a periodic calibration sound that covers a calibrationfrequency range, where the periodic calibration sound comprises (i) afirst component that includes noise at frequencies between a minimum ofthe calibration frequency range and a first threshold frequency, and(ii) a second component that sweeps through frequencies between a secondthreshold frequency and a maximum of the calibration frequency range.

In another aspect, a device is provided. The device includes a networkinterface, at least one processor, a data storage, and program logicstored in the data storage and executable by the at least one processorto perform operations. The operations may include receiving, via thenetwork interface, a command that instructs the playback device to emita calibration sound and responsively causing the one or more speakers toemit a periodic calibration sound that covers a calibration frequencyrange, where the periodic calibration sound comprises (i) a firstcomponent that includes noise at frequencies between a minimum of thecalibration frequency range and a first threshold frequency, and (ii) asecond component that sweeps through frequencies between a secondthreshold frequency and a maximum of the calibration frequency range.

In yet another aspect, a non-transitory computer readable memory isprovided. The non-transitory computer readable memory has stored thereoninstructions executable by a computing device to cause the computingdevice to perform operations. The operations may include receiving, viathe network interface, a command that instructs the playback device toemit a calibration sound and responsively causing the one or morespeakers to emit a periodic calibration sound that covers a calibrationfrequency range, where the periodic calibration sound comprises (i) afirst component that includes noise at frequencies between a minimum ofthe calibration frequency range and a first threshold frequency, and(ii) a second component that sweeps through frequencies between a secondthreshold frequency and a maximum of the calibration frequency range.

Further example techniques may involve multiple playback devicesemitting a calibration sound. In one aspect, a method is provided. Themethod may involve detecting a trigger condition that initiatescalibration of a plurality of playback devices. The method may alsoinvolve sending, to a first playback device of the plurality, a commandthat instructs the first playback device to repeatedly emit acalibration sound according to a sequence, where the calibration soundcycles through frequencies of a calibration frequency range, and where aduration of the calibration sound is proportional to the given number ofplayback devices in the plurality. The method may further involvesending, to one or more additional playback devices of the plurality,respective commands that instruct the one or more additional playbackdevices to repeatedly emit the respective calibration sound according tothe sequence, where the commands instruct the one or more additionalplayback devices to stagger emission of the calibration sounds such thateach emitted calibration sound is delayed relative to a precedingcalibration sound in the sequence. The method may also involvedetecting, via a microphone, the emitted calibration sounds.

In another aspect, a device is provided. The device includes a networkinterface, at least one processor, a data storage, and program logicstored in the data storage and executable by the at least one processorto perform operations. The operations may include detecting a triggercondition that initiates calibration of a plurality of playback devices.The operations may also include sending, to a first playback device ofthe plurality, a command that instructs the first playback device torepeatedly emit a calibration sound according to a sequence, where thecalibration sound cycles through frequencies of a calibration frequencyrange, and where a duration of the calibration sound is proportional tothe given number of playback devices in the plurality. The operationsmay further include sending, to one or more additional playback devicesof the plurality, respective commands that instruct the one or moreadditional playback devices to repeatedly emit the respectivecalibration sound according to the sequence, where the commands instructthe one or more additional playback devices to stagger emission of thecalibration sounds such that each emitted calibration sound is delayedrelative to a preceding calibration sound in the sequence. Theoperations may also include detecting, via a microphone, the emittedcalibration sounds.

In yet another aspect, a non-transitory computer readable memory isprovided. The non-transitory computer readable memory has stored thereoninstructions executable by a computing device to cause the computingdevice to perform operations. The operations may include detecting atrigger condition that initiates calibration of a plurality of playbackdevices. The operations may also include sending, to a first playbackdevice of the plurality, a command that instructs the first playbackdevice to repeatedly emit a calibration sound according to a sequence,where the calibration sound cycles through frequencies of a calibrationfrequency range, and where a duration of the calibration sound isproportional to the given number of playback devices in the plurality.The operations may further include sending, to one or more additionalplayback devices of the plurality, respective commands that instruct theone or more additional playback devices to repeatedly emit therespective calibration sound according to the sequence, where thecommands instruct the one or more additional playback devices to staggeremission of the calibration sounds such that each emitted calibrationsound is delayed relative to a preceding calibration sound in thesequence. The operations may also include detecting, via a microphone,the emitted calibration sounds.

The specification is presented largely in terms of illustrativeenvironments, systems, procedures, steps, logic blocks, processing, andother symbolic representations that directly or indirectly resemble theoperations of data processing devices coupled to networks. These processdescriptions and representations are typically used by those skilled inthe art to most effectively convey the substance of their work to othersskilled in the art. Numerous specific details are set forth to provide athorough understanding of the present disclosure. However, it isunderstood to those skilled in the art that certain embodiments of thepresent disclosure can be practiced without certain, specific details.In other instances, well known methods, procedures, components, andcircuitry have not been described in detail to avoid unnecessarilyobscuring aspects of the embodiments. Accordingly, the scope of thepresent disclosure is defined by the appended claims rather than theforgoing description of embodiments.

When any of the appended claims are read to cover a purely softwareand/or firmware implementation, at least one of the elements in at leastone example is hereby expressly defined to include a tangible,non-transitory medium such as a memory, DVD, CD, Blu-ray, and so on,storing the software and/or firmware.

We Claim:
 1. A first playback device comprising: one or more processors;a computer-readable medium having stored thereon instructions that, whenexecuted by the one or more processors, cause the first playback deviceto perform a method comprising: forming a first synchronous playbackgroup with one or more second playback devices; while formed into thefirst synchronous playback group, repeatedly playing back a firstcalibration sound according to a first sequence contemporaneously withplayback of the first calibration sound by the one or more secondplayback devices, wherein the first sequence comprises the firstcalibration sound cycling through frequencies of a calibration frequencyrange, and wherein playback devices of the first synchronous playbackgroup stagger playback of the first calibration sound; forming a secondsynchronous playback group with one or more third playback devices,wherein at least one of the third playback devices is different from atleast one of the second playback devices; while formed into the secondsynchronous playback group, repeatedly playing back a second calibrationsound according to a second sequence contemporaneously with playback ofthe second calibration sound by the one or more third playback devices,wherein the second sequence comprises the second calibration soundcycling through frequencies of the calibration frequency range, andwherein playback devices of the second synchronous playback groupstagger playback of the second calibration sound; receiving datarepresenting audio processing coefficients, the audio processingcoefficients comprising (i) first audio processing coefficients that arebased on playback of the first calibration sound while formed into thefirst synchronous playback group and (ii) second audio processingcoefficients that are based on playback of the second calibration soundwhile formed into the first synchronous playback group; applying thefirst audio processing coefficients to playback of audio content whenformed into the first synchronous playback group; and applying thesecond audio processing coefficients to playback of audio content whenformed into the second synchronous playback group.
 2. The first playbackdevice of claim 1, wherein the playback devices of the first synchronousplayback group play back the first calibration sound according to thefirst sequence for a first duration of time that is proportional to anumber of the playback devices of the first synchronous playback group,and wherein the playback devices of the second synchronous playbackgroup play back the second calibration sound according to the firstsequence for a second duration of time that is proportional to a numberof the playback devices of the second synchronous playback group.
 3. Thefirst playback device of claim 1, wherein the first calibration soundand the second calibration sound comprise (i) a first component thatincludes noise frequencies between a minimum of the calibrationfrequency range and a first threshold frequency, and (ii) a secondcomponent that sweeps through frequencies between a second thresholdfrequency and a maximum of the calibration frequency range.
 4. The firstplayback device of claim 1, wherein the first calibration sound and thesecond calibration sound comprise a baseline tone that coversfrequencies of the calibration frequency range within a given duration,and wherein the method further comprises: selecting the firstcalibration sound from among multiple calibration sounds, the selectedfirst calibration sound being substantially proportional in duration toa product of the given duration of the baseline tone and a number ofplayback devices in the first synchronous playback group; and selectingthe second calibration sound from among the multiple calibration sounds,the selected second calibration sound being substantially proportionalin duration to a product of the given duration of the baseline tone anda number of playback devices in the second synchronous playback group.5. The first playback device of claim 1, wherein the first calibrationsound and the second calibration sound comprise a baseline tone thatcovers frequencies of the calibration frequency range within a givenduration, wherein the playback devices of the first synchronous playbackgroup stagger playback of the first calibration sound by a delay that isbased on the given duration of the baseline tone, and wherein theplayback devices of the second synchronous playback group staggerplayback of the second calibration sound by the delay that is based onthe given duration of the baseline tone.
 6. The first playback device ofclaim 1, wherein the method further comprises: receiving, via a networkinterface from a mobile device, data representing one or more firstcommands to repeatedly play back the first calibration sound accordingto the first sequence contemporaneously with playback of the firstcalibration sound by the one or more second playback devices, whereinthe playback devices of the first synchrony group repeatedly play backthe first calibration sound according to the second sequence in responseto the data representing the one or more first commands; and receiving,via the network interface from the mobile device, data representing oneor more second commands to repeatedly play back the second calibrationsound according to the second sequence contemporaneously with playbackof the second calibration sound by the one or more third playbackdevices, wherein the playback devices of the second synchrony grouprepeatedly play back the second calibration sound according to thesecond sequence in response to the data representing the one or moresecond commands.
 7. The first playback device of claim 6, whereinreceiving data representing audio processing coefficients comprisingreceiving, via the network interface from the mobile device, the datarepresenting the audio processing coefficients.
 8. A tangible,non-transitory computer-readable medium having stored thereoninstructions that, when executed by one or more processors, cause afirst playback device to perform a method comprising: forming a firstsynchronous playback group with one or more second playback devices;while formed into the first synchronous playback group, repeatedlyplaying back a first calibration sound according to a first sequencecontemporaneously with playback of the first calibration sound by theone or more second playback devices, wherein the first sequencecomprises the first calibration sound cycling through frequencies of acalibration frequency range, and wherein playback devices of the firstsynchronous playback group stagger playback of the first calibrationsound; forming a second synchronous playback group with one or morethird playback devices, wherein at least one of the third playbackdevices is different from at least one of the second playback devices;while formed into the second synchronous playback group, repeatedlyplaying back a second calibration sound according to a second sequencecontemporaneously with playback of the second calibration sound by theone or more third playback devices, wherein the second sequencecomprises the second calibration sound cycling through frequencies ofthe calibration frequency range, and wherein playback devices of thesecond synchronous playback group stagger playback of the secondcalibration sound; receiving data representing audio processingcoefficients, the audio processing coefficients comprising (i) firstaudio processing coefficients that are based on playback of the firstcalibration sound while formed into the first synchronous playback groupand (ii) second audio processing coefficients that are based on playbackof the second calibration sound while formed into the first synchronousplayback group; applying the first audio processing coefficients toplayback of audio content when formed into the first synchronousplayback group; and applying the second audio processing coefficients toplayback of audio content when formed into the second synchronousplayback group.
 9. The tangible, non-transitory computer-readable mediumof claim 8, wherein the playback devices of the first synchronousplayback group play back the first calibration sound according to thefirst sequence for a first duration of time that is proportional to anumber of the playback devices of the first synchronous playback group,and wherein the playback devices of the second synchronous playbackgroup play back the second calibration sound according to the firstsequence for a second duration of time that is proportional to a numberof the playback devices of the second synchronous playback group. 10.The tangible, non-transitory computer-readable medium of claim 8,wherein the first calibration sound and the second calibration soundcomprise (i) a first component that includes noise frequencies between aminimum of the calibration frequency range and a first thresholdfrequency, and (ii) a second component that sweeps through frequenciesbetween a second threshold frequency and a maximum of the calibrationfrequency range.
 11. The tangible, non-transitory computer-readablemedium of claim 8, wherein the first calibration sound and the secondcalibration sound comprise a baseline tone that covers frequencies ofthe calibration frequency range within a given duration, and wherein themethod further comprises: selecting the first calibration sound fromamong multiple calibration sounds, the selected first calibration soundbeing substantially proportional in duration to a product of the givenduration of the baseline tone and a number of playback devices in thefirst synchronous playback group; and selecting the second calibrationsound from among the multiple calibration sounds, the selected secondcalibration sound being substantially proportional in duration to aproduct of the given duration of the baseline tone and a number ofplayback devices in the second synchronous playback group.
 12. Thetangible, non-transitory computer-readable medium of claim 8, whereinthe first calibration sound and the second calibration sound comprise abaseline tone that covers frequencies of the calibration frequency rangewithin a given duration, wherein the playback devices of the firstsynchronous playback group stagger playback of the first calibrationsound by a delay that is based on the given duration of the baselinetone, and wherein the playback devices of the second synchronousplayback group stagger playback of the second calibration sound by thedelay that is based on the given duration of the baseline tone.
 13. Thetangible, non-transitory computer-readable medium of claim 8, whereinthe method further comprises: receiving, via a network interface from amobile device, data representing one or more first commands torepeatedly play back the first calibration sound according to the firstsequence contemporaneously with playback of the first calibration soundby the one or more second playback devices, wherein the playback devicesof the first synchrony group repeatedly play back the first calibrationsound according to the second sequence in response to the datarepresenting the one or more first commands; and receiving, via thenetwork interface from the mobile device, data representing one or moresecond commands to repeatedly play back the second calibration soundaccording to the second sequence contemporaneously with playback of thesecond calibration sound by the one or more third playback devices,wherein the playback devices of the second synchrony group repeatedlyplay back the second calibration sound according to the second sequencein response to the data representing the one or more second commands.14. The tangible, non-transitory computer-readable medium of claim 13,wherein receiving data representing audio processing coefficientscomprising receiving, via the network interface from the mobile device,the data representing the audio processing coefficients.
 15. A method tobe performed by a first playback device, the method comprising: forminga first synchronous playback group with one or more second playbackdevices; while formed into the first synchronous playback group,repeatedly playing back a first calibration sound according to a firstsequence contemporaneously with playback of the first calibration soundby the one or more second playback devices, wherein the first sequencecomprises the first calibration sound cycling through frequencies of acalibration frequency range, and wherein playback devices of the firstsynchronous playback group stagger playback of the first calibrationsound; forming a second synchronous playback group with one or morethird playback devices, wherein at least one of the third playbackdevices is different from at least one of the second playback devices;while formed into the second synchronous playback group, repeatedlyplaying back a second calibration sound according to a second sequencecontemporaneously with playback of the second calibration sound by theone or more third playback devices, wherein the second sequencecomprises the second calibration sound cycling through frequencies ofthe calibration frequency range, and wherein playback devices of thesecond synchronous playback group stagger playback of the secondcalibration sound; receiving data representing audio processingcoefficients, the audio processing coefficients comprising (i) firstaudio processing coefficients that are based on playback of the firstcalibration sound while formed into the first synchronous playback groupand (ii) second audio processing coefficients that are based on playbackof the second calibration sound while formed into the first synchronousplayback group; applying the first audio processing coefficients toplayback of audio content when formed into the first synchronousplayback group; and applying the second audio processing coefficients toplayback of audio content when formed into the second synchronousplayback group.
 16. The method of claim 15, wherein the playback devicesof the first synchronous playback group play back the first calibrationsound according to the first sequence for a first duration of time thatis proportional to a number of the playback devices of the firstsynchronous playback group, and wherein the playback devices of thesecond synchronous playback group play back the second calibration soundaccording to the first sequence for a second duration of time that isproportional to a number of the playback devices of the secondsynchronous playback group.
 17. The method of claim 15, wherein thefirst calibration sound and the second calibration sound comprise (i) afirst component that includes noise frequencies between a minimum of thecalibration frequency range and a first threshold frequency, and (ii) asecond component that sweeps through frequencies between a secondthreshold frequency and a maximum of the calibration frequency range.18. The method of claim 15, wherein the first calibration sound and thesecond calibration sound comprise a baseline tone that coversfrequencies of the calibration frequency range within a given duration,and wherein the method further comprises: selecting the firstcalibration sound from among multiple calibration sounds, the selectedfirst calibration sound being substantially proportional in duration toa product of the given duration of the baseline tone and a number ofplayback devices in the first synchronous playback group; and selectingthe second calibration sound from among the multiple calibration sounds,the selected second calibration sound being substantially proportionalin duration to a product of the given duration of the baseline tone anda number of playback devices in the second synchronous playback group.19. The method of claim 15, wherein the first calibration sound and thesecond calibration sound comprise a baseline tone that coversfrequencies of the calibration frequency range within a given duration,wherein the playback devices of the first synchronous playback groupstagger playback of the first calibration sound by a delay that is basedon the given duration of the baseline tone, and wherein the playbackdevices of the second synchronous playback group stagger playback of thesecond calibration sound by the delay that is based on the givenduration of the baseline tone.
 20. The method of claim 15, wherein themethod further comprises: receiving, via a network interface from amobile device, data representing one or more first commands torepeatedly play back the first calibration sound according to the firstsequence contemporaneously with playback of the first calibration soundby the one or more second playback devices, wherein the playback devicesof the first synchrony group repeatedly play back the first calibrationsound according to the second sequence in response to the datarepresenting the one or more first commands; and receiving, via thenetwork interface from the mobile device, data representing one or moresecond commands to repeatedly play back the second calibration soundaccording to the second sequence contemporaneously with playback of thesecond calibration sound by the one or more third playback devices,wherein the playback devices of the second synchrony group repeatedlyplay back the second calibration sound according to the second sequencein response to the data representing the one or more second commands.